High temperature lubricants and phosphorus containing polymers



United States Patent Ofiice 3,169,925 Patented 1 611.16, 1965 Delaware a No Drawing. Filed lune 26, E61, Ser. No. 119,:32 Claims. (El. 25249.8)

This invention relates to lubricating compositions, more particularly, it relates to lubricating compositions es pecially designed for use at elevated temperatures and under high load conditions.

Aircraft and gas turbine engine lubricants require special properties, such as high temperature stability and oxidation stability which are not possessed to a sufficient degree by a conventional lubricant. They must possess a high viscosity index in order to provide adequate lubrication under a wide range of conditions. They must be thermally stable and must be either stable to oxidation or amenable to stabilization against oxidation and must retain these properties after operation for extended periods at high temperatures. While it is preferred that they have low pour points, the mechanisms containing them may be heated in such a way as to maintaln high pour point materials in a fluid condition durmg down time or cold operating periods.

In addition to being stable to oxidation, one of the essential properties demanded of lubricants is that they operate mechanisms which at times may be subject to high loads (extreme pressures). Very little is known of the performance of extreme pressure additives under the high temperature conditions contemplated for uses such as gas turbine engine lubricants and the like.

One of the most promising types of synthetic lubricants recently investigated for the above purposes is the class of polyphenyl ethers wherein unsubstituted ethers or others substituted with tertiary butyl or alpha-cumyl radicals are utilized. Such ethers have been found to have extremely high thermal stability and satisfactory lubricity under most operating conditions. Their performancein high speed bearings appears to be good under most conditions. However, at extremely high temperatures, their lubricating properties may be deficient for some applications. Although their gear performance is comparable to that of mineral oils of similar viscosity, at high temperatures where viscosities are low, their load carrying ability is below desired levels.

Most conventional extreme pressure agents are unsuitable for use in environments envisioned for the polyphenyl ethers so that substantially nothing in the way of prediction is possibly based on previous experience with such materials. This is true since the high temperatures under which polyphenyl ethers are often utilized either cause decomposition of most extreme pressure agents or cause them to undergo phenomena which do not appear at temperatures at which they may be employed in mineral or other synthetic oils. It was found that many prospective additives which were quite acceptable in other media and at lower temperatures were not eifective in polyphenyl ethers.

Criteria must be set up for such material to be satisfactory; first, it should have a high enough molecular weight to avoid volatility losses at excessive temperatures. It should have an aromatic structure for maximum stability with respect to oxidation, radiation and thermal stresses. It should have a minimum effect upon the stability of the base oil and, of course, should exhibit extreme pressure properties at the elevated temperatures contemplated.

It has been found that many potential extreme pressure agents, useful in other media at lower temperatures, actually exert a pro-wear effect at low concentrations in the lubricants to be considered here, namely the polyphenyl ethers. In fact, this adverse pro-wear eifect is distressingly noticeable in the polyphenyl ethers when only small amounts of otherwise satisfactory extreme pressure agents are utilized. This can be overcome, of course, by increasing the amount of extreme pressure agents, but always at the expense of high temperature stability such as it is desired to achieve with the otherwise extremely stable polyphenyl ethers.

It is an object of the present invention to provide im proved lubricating compositions especially useful for operation of engines, motors and moving metallic elements at high operating temperatures and under high loads. It is a particular object of this invention to extend the range of bearing pressures under which polyphenyl ethers may be utilized, particularly at operating temperatures exceeding about 450 F. A particular object is to provide novel phosphorus-containing polymeric materials. A further particular object is to provide extreme high temperature synthetic lubricants containing effective and stable extreme pressure additives which do not contribute to oxygen sensitivity. Other objects will become apparent during the following detailed description of the invention.

Now, in accordance with the present invention, novel phosphorus compounds are provided, having the general configuration Ar n Ar wherein n is an average integer between about 5 and about 500 (preferably 10-150) and the radicals Ar, Ar and Ar" are selected from the group consisting of phenyl, biphenyl and phenoxyphenyl radicals, each radical hearing substituents of the group consisting of hydrogen, tertiary butyl, phenyl, phenoxy phenyl and biphenyl radicals aside from those bonds which are satisfied by connection with other parts of the polymeric molecule.

Still in accordance with the present invention, compositions are provided which are especially useful for lubricating purposes at elevated temperatures and high loads. These compositions comprise a major proportion of certain polyphenyl ethers as defined more fully hereinafter and minor proportions, eliective to increase the extreme pressure properties thereof at elevated temperatures, between about 0.05 and 5% by weight, of a phosphorus polymer having the above configuration.

The polymers of this invention having the general configuration given above preferably have between about 10 and 50 units as represented within the bracket of the general formula. The aromatic groups represented Ar,

Ar, Ar" may be the same or different from each other. Moreover, mixtures of each of the individually designated aromatic radicals may be present within a single molecule. While the preferred species of the polymeric material comprises that in which all of the aromatic radicals designated Ar, Ar, Ar" comprise phenoxyphenyl radicals, other suitable polymers are consituted by those in which the radicals Ar, are phenyl, phenoxy phenyl or biphenyl and the substituents Ar, may be varied in like manner. The substituent Ar may be phenyl, phenoxy phenyl or biphenyl independent of the particular aromatic substituents present as the aryloxy groups other wise in the molecule. While unsubstituted phenyl rings are preferred, certain restricted substituents may be utilized to replace hydrogen radical on the ring such as tertiary butyl, phenyl, or phenoxy radicals, in addition to alpha cumyl radicals.

The polymeric materials are preferably prepared by the following sequence of steps:

Phosphorus oxychloride is heated with a mouohydric phenol to eliminate HCl and form an aryloxy phosphorus oxydichloride according to the following general reaction:

For this purpose and in accordance with the abovere strictions relative to substituents which may be tolerated on the phenoxy radicals directlyattached to the phosphorus, atom, the following monohydric phenols may be employed:

MONOHYDREC PHENOLS Phenol flgt-bliltygphelnol p eny p sun 2 phenoxyphenol alpha cumylphenol 2,4,-bis(tert butyDphenol 3,4-diphenyl phenol 2,6-diphenoxyphenol and mixtures thereof more dihydric' phenols according to the following re-- action According to the above reaction, a dihydric phenol and the dichloro phosphorus compound are heated in the presence of basic catalyst such as pyridine or a trialkyl amine (trimethyl amine) to obtain a polymeric linear compound or mixture of compounds containing terminal chloride radicals. Suitable dihydric phenols which may be employed for the above purpose and at the same time meet the limitations relative to substituents as defined herein before are as follows:

DIHYDRIC PHENOLS The above reaction is preferably carried out by dispersing the dihydric phenol in a solvent which may be the alkaline catalyst such as pyridine and gradually adding thereto the monoaryl phosphorusoxy dichloride. A limited reaction occurs which raises the temperature to a slight extent; The reaction mixture is then heated,

preferably under reflux, for a time of %4 hours at tem-- per-atures varying from about to about 200 C., preferably 90-130" C. Thereafter a further quantity of monohydric phenols (which is the same or a different phenol from that originally employed as described according to reaction 1 above), is added in an amount to react stoichiometrically with any remaining chlorine radicals contained in the molecule of the polymeric materials formed The third equation according to the reaction 2 above. can be represented as follows:

OH ii i O1 -1| -o 0 .'i C1+ O O l I r t t -o -1 -o 0 -P-O The product of these three reactions is the polymer as defined hereinbefore. It contains substantially no halogen and any substituents other than hydrogen directly attached to carbon atoms on the ring (aside from the one valence which is directly attached to linking oxygen atoms) comprise the substituents listed hereinbefore.

The final reaction (Equation 3) preferably is carried out by heating the reaction mixture containing additional quantities of monohydric phenol at elevated temperatures preferably under reflux of a solvent present, such as pyridine, for a time sufi'icient to cause replacement of any halogen atoms present in the polymer with aryloxy radicals. Generally, this would be temperatures between about and 200 0., preferably -130 C., for periods varying from about %-4 hours. Thereafter the product may be'purified and isolated by adding a solvent therefore such as benzene, extracting with water, and then aqueous bicarbonate and/ or HCl, and subsequently isolating the polymer such as by precipitation with petroleum ether.

The polymers of this invention are useful for a number of purposes such as high temperature lubricants perse, as thickeners for lubricating oils, as water proofing agents for high temperature gelling agents sucheas clay, silica and the like, but are especially useful as load bearing additives for lubricants and in particular for the polyphenyl others.

In accordance with one aspect of the invention, the polyphenyl ethers as more fully defined hereinafter are surprisingly responsive to the presence of minor amounts (ODS-5%) by weight of the above phosphorus polymers.

The polyphenyl ethers subject torimprovement with the above class of polymeric phosphorus compounds are confined to varieties which are unsubstituted polyphenyl ethers or those which are substituted with either tertiary butyl radicals or with alpha-cumyl radicals or both. The

presence of other substituents, such as methyl radicals and the like, is undesirable and is not contemplated as falling within the scope of the present invention. This is due to the fact that the presence of these undesired substituents causes the formation of polyphenyl ethers which are unstable under the high temperature conditions contemplated.

The unsubstituted polyphenyl ethers have been found to be outstandingly stable but may be improved in their operating life at temperatures above 400 F. by the presence of the subject classes of additives as described herein. However, the major use of the present invention is with respect to the two other types of polyphenyl ethers, namely, those containing tertiary butyl substituents, alpha-cumyl substituents or both. Mixtures of the unsubstituted polyphenyl ethers with the tertiary butyl or alpha-cumyl substituted ethers is contemplated.

It is furthermore contemplated to utilize polyphenyl ethers containing ortho, meta or para linkages and preferably species containing a mixture of these linkages within the same molecule so as to promote relatively low pour points in the materials. The meta linkage has been found to be that which produces polyphenyl ethers having the lowest pour points. Consequently, in accordance with the present invention, compositions are provided which are especially useful for lubricating purposes and have good lubricating oil pour points comprising certain restricted classes of polyphenyl ethers, at least two of said ethers being present in the composition and at least one-third of the linkages between phenyl radicals being in meta positions relative to each other. More particularly, and in order to maintain the maximum thermal stability, the polyphenyl ethers with which this invention is concerned are restricted to the unsubstituted polyphenyl ethers and those containing tertiarybutyl and/or alpha-cumyl substituents as well as ethers in which up to'two-thirds of the oxygen linkages are replaced With isopropylidene linkages. Still in accordance with this invention it is preferred that the mixture of polyphenyl ethers have an average of 3-8 phenyl radicals per molecule and preferably between 4 and 6 phenyl radicals per molecule.

A preferred form of the present invention comprises a mixture of the subject classes of polyphenyl ethers wherein at least one member of the mixture contains both meta linkages between phenyl groups and ortho or para linkages within the same molecule. This is an especially effective way of reducing the pour point of the mixture in addition to mixing two non-identical polyphenyl ethers. The effect is magnified when the proportion of meta linkages is at least 50% of those present and preferably between 60 and 90% of the linkages, the remaining being either ortho or para linkages, preferably para. When the polyphenyl ether comprises one in which there is an oxygen linkage between two groups of polyphenyl linkages, it is sufiicient that at least 50% of the linkages other than the one specified oxygen linkage are in the meta position relative to said ether linkage. As stated hereinbefore, these additional linkages between phenyl radicals may be either oxygen or isopropylidene. Table I, which follows, lists typical polyphenyl ethers which may comprise principal or minor components in the mixtures under consideration.

Table I.P0lyphenyl ethers Bis (meta-phenoxyphenyl) ether Bis (para-phenoxyphenyl) ether Bis ortho-phenoxyphenyl) ether meta-Bis (meta-phenoxyphenoxy) benzene meta-Bis (para-phenoxyphenoxy) benzene para-Bis (meta-phenoxyphenoxy) benzene 1- (meta-phenoxyphenoxy) -3- [meta (meta-tert-butyL phenoxy) phenoxy] benzene 1- [meta(meta-alpha-cumyl phenoxy) phenoxy] -3- (metaphenoxyphen oxy) benzene 1- [meta (meta-tert-butylphenoxy) phenoxy] -3- [para para-tert-butylphenoxy ph enoxy] benzene It is preferred that from the above types of polyphenyl ethers at least 50% of the mixture be a species either containing nothing but meta linkages or wherein at least about 60% or" the mixture comprising the lubricating composition be a species of polyphenyl ether wherein at least about two-thirds of the linkages between phenyl radicals are in the meta position relative to each other. Furthermore, it is preferred that at least about 25% (e.g., 25-75% by weight) of the composition be unsubstituted polyphenyl ethers containing nothing but oxygen iinkages between phenyl radicals and bearing no substituents on the carbocyclic rings other than hydrogen.

When utilizing mixtures of unsubstituted polyphenyl ethers with the tertiary butyl or alpha-cumyl substituted polyphenyl ethers, it is preferred that the composition contain from 10 to of unsubstituted ethers containing 2-6 phenyl radicals per molecule together with 90-10% by Weight based on the total composition of the substituted polyphenyl ethers as defined above. The principal function of the unsubstituted polyphenyl ethers is to enhance the outstanding high-temperature stability which this class of compounds has been found to exhibit. For a given configuration, the substituted polyphenyl ethers as outlined above impart low melting points and in mixture with the unsubstituted polyphenyl ethers causes the melting point of the entire composition to be substantially lower than that of the unsubstituted polyphenyl ethers themselves.

One of the unexpected features of utilizing the subject phosphorus polymers as extreme pressure agents in polyphenyl ether comprises their load bearing capacity even at low concentrations. The mechanism by which the polymers perform their function of imparting extreme pressure activity to the compositions is not fully understood, but is believed to be dependent at least in part upon the strong absorption on a metal surface of the highly polymeric substances. Consequently, one additional feature of the invention comprises precoating the metal bearing with phosphorus polymers after which the bearings are lubricated with polyphenyl ethers containing replenishing amounts of the phosphorus polymeric materials.

The following examples illustrate the preparation of the phosphorus polymers.

Table H.Polymer preparation Time of Temp. of Yield of Time of Temp. of Yield of Average Monohydric Heating Heating POClz- Dihydrio Polymeri- Polymeri- Polymer, Molecular Polymer Phenol with with OAr, Phenol zation, zation, Percent Weight P001 P001 C. Percent hours C. (Cryohours scopie) 1 Phenol 21 120-170 51 Hydroqui- 2 35-115 91 5, 500

none. 2 Phenoxy- 22 -160 42 do 2 35-115 90. 5 2, 420

phenol. 3 do 22 110-160 42 p-DiphenoL- 2 50-115 87 4 do 22 110-100 42 Bis(p-hydrox- 2 50-120 84 7, 900

yphenyl)- Ether.

The above polymers are characteristically rubbery,

resins or crumbly, friable solids having limited solubility in polyphenyl ethers and soluble in aromatic solvents such as benzene and the like.

The polymers preparedand described above were tested in blends with typical mixture of polyphenyl ethers mainly mixed (isomeric) bis(phenoxyphenoxy) benzenes. Gear Tests were conducted, utilizing spur gears at a temperature of about 400 F., 3200 r.p.m., minute runs at 288 lbs./ in. 1021 increments. The failure load in pounds per inch as evidenced by abrasion is given for a number of additiveswithin the present invention in Table HIJ Table III.-Spur gear results Failure Load, lb .lin. Additive in C oncen- Bis (phenoxyphenoxy)benzene tration,

Percent w. Onset of Abrasion Scoring 7 None 1, 004 I 860 Phenoxyphenyl Phosphate-Bis (phydroxyphenyl) Ether Polymer 2. 5 2, 495 l, 416 Do 0.5 l, 984 1, 416

Illustrating the significance of concentration of additives upon the successfulimprovementin extreme pressure properties, comparative tests Were run utilizing the.

same mixture of polyphenyl ethers modified with varying concentrations of some of the above polymers in a 4-ball test'under 10 kilogram load at 400 F. and a speed 1324 rpm. The following results were obtained:

Table 1V.Summary of four-ball wear tests [400F., 1325 r.p.m., 10 kg. load, 0.5 inch diameter 52-100 steel balls] I claim as my invention:

1. A lubricating composition comprising a major proportion of a polyphenyl ether base having from 3 to 8 phenyl rings per molecule selectedfrom the group consisting of unsubstituted ethers,- tert-butyl substituted ethers, and alpha-cumyl substituted ethers, and mixtures thereof, and an effective load-bearing amount of 0.05% to about 5% by weight of a phosphorus polymer of the configuration:

wherein Ar, Ar, and Ar are aromatic radicals of the group consisting of phenyl, biphenyl and phenoxyphenyl, each phenyl radical having as substituents on the ring only I 11 Ar substituents of the group consisting of hydrogen, tertiary butyl, phenyl, alpha-cumyl and phenoxy radicals, and

n is an average integer from 5 to 500.

2. A lubricating composition comprising a major proportion of unsubstituted polyphenyl ethers having 3 to 8 phenyl rings per molecule and 0.1 to 2.5% by weight of the polymer according to claim 1.

3. The lubricating composition of claim 2 wherein the polyphenyl ethers have 4 to 6 phenyl rings per molecule.

4. The lubricating composition of claim 1 wherein n is 10-50 and Ar, Ar, and Ar are phenyl radicals.

5. The lubricating composition of claim 2 wherein n is 1050 and Ar, Ar, and Ar" are phenyl radicals.

References Cited by theExaminer UNITED STATES PATENTS 2,058,394 10/36 Arvin 260--47 2,435,252 2/48 Toy 260--6l 2,616,873 11/52 Cass 26061 2,636,876 4/53 Zenftman et al. 260' -61 2,658,871 11/53 Smith et al. 252-49.8 2,964,477 12/60 Pilat et al. 25249.8

- FOREIGN PATENTS 679,834 9/52 Great Britain.

851,651 a 10/60 Great Britain.

DANIEL E. WY MAN, Primary Examinen JULIUS GREENWALD, Examiner. 

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR PROPORTION OF A POLYPHENYL ETHER BASE HAVING FROM 3 TO 8 PHENYL RINGS PER MOLECULE SELECTED FROM THE GROUP CONSISTING OF UNSUBSTITUTED ETHERS, TERT-BUTYL SUBSTITUTED ETHERS, AND ALPHA-CUMYL SUBSTITUTED ETHERS, AND MIXTURES THEREOF, AND AN EFFECTIVE LOAD-BEARING AMOUNT OF 0.05% TO ABOUT 5% BY WEIGHT OF A PHOSPHORUS POLYMER OF THE CONFIGURATION: 